Hello Vladimir,.. it maybe your "Scene" or Lighting? .. a easy way to see if it is either,. change/toggle it to another Scene, that is, from "3 Point Beige" to "3 Point Faded".. or my favorite "Reflective Floor Black".

..or,.. maybe.. your "Template File"..used with the STEP file creation is pointing at a different directory.. that is, the latest version is using the latest default template which includes a Scene (w/lights) that are dimmed?